本研究旨在利用壓力螢光感測塗料(Pressure sensitive paint; PSP)量測凹槽模型於穿音速流場中的表面壓力分佈，目的在於探討穿音速流之中凹槽的流場現象。凹槽流於流體力學領域為一典型的研究題目，而飛行載具上的投彈孔與起落架也經常設計成凹槽的樣式。高速流經凹槽的氣流於凹槽內產生的複雜流場將對飛行載具投擲彈藥的精確度與飛行安全產生影響，故凹槽流的研究對飛行載具的設計與改進有著重大的影響。
本研究量測的凹槽模型為長度深度比(L/h)為6.14與21.5的矩形凹槽，凹槽軸向與自由流方向呈10°、30°、45°的夾角，穿音速風洞自由流速度設定為馬赫數0.83，紊流邊界層厚度約為7 mm。本研究應用的壓力螢光感測塗料為一種藉由螢光分子針對環境氧氣濃度變化產生螢光亮度變化機制來量測壓力的技術，透過激發光的照射與CCD相機接收放射光，再由影像中每一像素之亮度變化計算其壓力值，即可測得全域性壓力分佈。有別於傳統實驗中以壓力管量測模型表面壓力的方法，壓力螢光感測塗料技術具有高空間解析度、優異的複雜幾何模型表面適用性、干擾流場程度低、製備容易與成本較低等優勢。本研究以高分子材料與二氧化矽粉末製造出能夠吸附螢光分子的多孔性壓力螢光感測塗料，並成功應用壓力螢光感測塗料實驗技術量測出凹槽模型於0.83馬赫流場中的全域性壓力分佈。
長度深度比為6.14的凹槽屬於開放式凹槽，較深的幾何設計使剪應力層橫渡凹槽上方，並驅動凹槽內流體產生一巨大渦漩。此流場現象造成凹槽內中心為局部低壓帶，與凹槽後緣處的高壓帶壓差約為5 kPa。長度深度比為21.5的凹槽屬於封閉式凹槽，剪應力層於凹槽前緣分離後便向下衝擊凹槽底部，使凹槽內部前緣處為局部低壓帶，後緣則因流體受阻而成為高壓帶，前後緣壓差約為10 kPa。凹槽內流場隨著軸向與自由流向轉角變化而有所影響。長深比為6.14的開放式凹槽中心局部低壓帶呈馬蹄狀彎曲，且隨著轉角由10°至45°變化，凹槽內壓力分佈的不對稱現象漸趨明顯;長深比為21.5的封閉式凹槽內靠近前緣的低壓帶則因轉角變化而隨著邊緣逐漸彎曲，且凹槽前後緣壓差由10 kPa降至約6 kPa。
綜合以上結果，本研究成功應用壓力螢光感測塗料於穿音速凹槽流表面壓力分佈的量測，並藉此探討凹槽流場三維特性與轉角造成的不對稱現象。軸向與側向壓力量測結果與前人以Kulite壓力感測器量測之結果比對後趨勢一致，並可提供詳細二維凹槽表面的壓力分佈，證明壓力螢光感測塗料應用於穿音速流場的可行性。

This study aims to investigate the flow field of transonic cavity flow by measuring the surface pressure distribution using pressure sensitive paint (PSP). A cavity flow has been a classic topic in fluid mechanics, and the cavities are considered as the weapon bays and the space for landing gears of modern aircrafts. A high-speed flow over a cavity causes a complex flow field, and the pressure variation inside the cavity could induce some problems of the accuracy of bomb dropping and the flight safety. Therefore, the study of cavity flow is important for designing of aircrafts.
This study discussed the characteristics for a transonic flow over rectangular cavities with different yaw angles. The free stream Mach number was 0.83 and the thickness of turbulent boundary layer was 7 mm. The ratios of length to depth for the rectangular cavities were 6.14 and 21.5, and the yaw angles were 10°, 30°and 45°. PSP is an experimental technique which can be used for surface pressure measurement. The mechanism of PSP measurement is based on photo luminescence and oxygen quenching. An excitation light and a CCD camera were used to excite the PSP sensor and capture the luminescence signal respectively. By calculating the variation of luminescence intensity ratio in every pixel in the acquired images, the global pressure distribution can be translated after applying the pressure calibration curve. In this research, polymer binder and TiO2 powders were used to prepare porous-based PSP. The porous-based PSP was applied to the cavity flow during transonic flow condition and the surface pressure distributions were also successfully measured in this study.
The cavity with length to depth ratio (L/h) of 6.14 can be considered as open-type cavity. Due to the relatively deep geometry, the flow goes over the cavity and the shear layer is formed over the cavity. The flow on the top of the cavity drives a large eddy inside the cavity and cause a relatively low-pressure region in the middle of the cavity, and a high pressure region identified near the trailing edge. The pressure at the low pressure region is about 5 kPa lower than the pressure near the trailing edge. The cavity with length to depth ratio (L/h) of 21.5 is considered as close-type cavity model. Because of the relatively shallow geometry, the flow expands from the leading edge and impinges on the floor. The flow then separates near the trailing face. The pressure different between the leading and trailing regions is about 10 kPa. The flow field inside the open- and closed-type cavities change as the yaw angle varying from 10° to 45°. For the L/h=6.14 open-type cavity, the relatively low-pressure region at the middle of the cavity is in a shape of hoof, and the asymmetrical pressure distribution becomes more obvious as the yaw angle increasing. For the L/h=21.5 closed-type cavity, the shape of the low-pressure region near the leading edge turns curved as the yaw angle increasing, and the pressure difference between the regions of leading and trailing edge reduces from 10 kPa to 6 kPa.
In this study, PSP is successfully applied to the measurement of surface pressure distribution in cavities flow with transonic flow condition. The three-dimensional flow characteristics and the asymmetrical phenomenon caused by the changing yaw angles are investigated. The pressure distribution along the chord wise and span wise center lines are compared with the experimental results measured by Kulite pressure transducer and good agreement are established. In addition, the PSP results can provide detailed and two dimensional profile of flow pattern for further analysis.

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